Adjustable magnetic devices and methods of using same

ABSTRACT

A system includes a first pedicle screw, a second pedicle screw, and an adjustable rod having an outer housing coupled to one of the first pedicle screw and the second pedicle screw, the outer housing having a threaded shaft secured to one end thereof extending along an interior portion thereof. The system further includes a hollow magnetic assembly disposed within the outer housing and having a magnetic element disposed therein, the hollow magnetic assembly having an internal threaded surface engaged with the threaded shaft, the magnetic assembly being coupled to the other of the first pedicle screw and the second pedicle screw, wherein the hollow magnetic assembly rotates in response to an externally applied magnetic field to thereby lengthen or shorten the distance between the first pedicle screw and the second pedicle screw.

RELATED APPLICATIONS

Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57.

FIELD OF THE INVENTION

The field of the invention generally relates to medical devices for treating spinal conditions.

BACKGROUND OF THE INVENTION

Degenerative disc disease affects 65 million Americans. Up to 85% of the population over the age of 50 will suffer from back pain each year. Degenerative disc disease (DDD) is part of the natural process of growing older. Unfortunately as we age, our intervertebral discs lose their flexibility, elasticity, and shock absorbing characteristics. The ligaments that surround the disc called the annulus fibrosis, become brittle and they are more easily tom. At the same time, the soft gel-like center of the disc, called the nucleus pulposus, starts to dry out and shrink. The combination of damage to the intervertebral discs, the development of bone spurs, and a gradual thickening of the ligaments that support the spine can all contribute to degenerative arthritis of the lumbar spine.

When degenerative disc disease becomes painful or symptomatic, it can cause several different symptoms, including back pain, leg pain, and weakness that are due to compression of the nerve roots. These symptoms are caused by the fact that worn out discs are a source of pain because they do not function as well as they once did, and as they shrink, the space available for the nerve roots also shrinks. As the discs between the intervertebral bodies start to wear out, the entire lumbar spine becomes less flexible. As a result, people complain of back pain and stiffness, especially towards the end of the day.

Depending on the severity and the condition, there are many ways to treat DDD patients with fusion being the most common surgical option. The estimated number of thoracolumbar fixation procedures in 2009 was 250,000. Surgery for degenerative disc disease usually involves removing the damaged disc. In some cases, the bone is then permanently joined or fused to protect the spinal cord. There are many different techniques and approaches to a fusion procedure. Some of the most common are ALIFs, PLIFs, TLIFs, XLIFs (lateral), etc. Almost all these techniques now involve some sort of interbody fusion device supplemented with posterior fixation (i.e. 360 fusion).

Another spinal malady that commonly affects patients is stenosis of the spine. Stenosis is related to the degeneration of the spine and typically presents itself in later life. Spinal stenosis can occur in a variety of ways in the spine. Most of the cases of stenosis occur in the lumbar region (i.e., lower back) of the spine although stenosis is also common in the cervical region of the spine. Central stenosis is a choking of the central canal that compresses the nerve tissue within the spinal canal. Lateral stenosis occurs due to the trapping or compression of nerves after it has left the spinal canal. This can be caused by bony spur protrusions, bulging, or herniated discs.

SUMMARY OF THE INVENTION

In one embodiment, a system includes a first pedicle screw, a second pedicle screw, and an adjustable rod having an outer housing coupled to one of the first pedicle screw and the second pedicle screw, the outer housing having a threaded shaft secured to one end thereof extending along an interior portion thereof. The system further includes a hollow magnetic assembly disposed within the outer housing and having a magnetic element disposed therein, the hollow magnetic assembly having an internal threaded surface engaged with the threaded shaft, the magnetic assembly being coupled to the other of the first pedicle screw and the second pedicle screw, wherein the hollow magnetic assembly rotates in response to an externally applied magnetic field to thereby lengthen or shorten the distance between the first pedicle screw and the second pedicle screw.

In another embodiment, a method for adjusting the amount of compression between two vertebral bodies includes securing a first pedicle screw to a first vertebra, securing a second pedicle screw to a second vertebra, and securing an adjustable rod between the first pedicle screw and the second pedicle screw, the adjustable rod having an outer housing coupled the first pedicle screw, the outer housing having a threaded shaft secured to one end thereof extending along an interior portion thereof, the adjustable rod further having a hollow magnetic assembly disposed within the outer housing and having a magnetic element disposed therein, the hollow magnetic assembly having an internal threaded surface engaged with the threaded shaft, the magnetic assembly being coupled to the second pedicle screw. The method further includes applying an external magnetic field to the adjustable rod to rotate the magnetic element.

In another embodiment, a system includes a first pedicle screw having a shank and a head, a second pedicle screw having a shank and a head, and a rod placed between the first pedicle screw and the second pedicle screw and contained within a housing. The system further includes a magnetic actuator disposed within the housing and associated with one of the first and second pedicle screws, the magnetic actuator having a rotatable magnetic element coupled to a bushing, the rotatable magnetic element configured to move relative to the housing in response to an externally applied magnetic field, wherein movement in a first direction frictionally engages the rod between the pedicle screw head and the bushing and wherein movement in a second direction disengages the rod from the pedicle screw head and the bushing.

In another embodiment, a system includes a first pedicle screw, a second pedicle screw, and a flexible spacer configured for placement between the first and second pedicle screws, the flexible spacer configured to adjust a compression or tension force between the first pedicle screw and second pedicle screw in response to an externally applied magnetic field.

In another embodiment, a device includes an interbody screw having first and second portions, the first portion having a threaded end and the second portion having a threaded end, at least one of the first and second portions being axially moveable with respect to the other in response to an externally applied magnetic field.

In another embodiment, an artificial disc device includes a body portion, a first adjustable member, and a second adjustable member arranged generally orthogonal to the first adjustable member, where the first and second adjustable members are configured to adjust a COR of the body portion in two orthogonal dimensions in response to an externally applied magnetic field.

In another embodiment, a distraction device interposed between two vertebral bodies includes first and second portions, one of the portions including a permanent magnet configured to rotate in response to an externally applied non-invasive magnetic field, the permanent magnet operatively coupled to a screw whereby rotation in one direction increases the height between the first and second portions.

In another embodiment, a distraction device implanted in a single vertebral body includes first and second portions, one the portions including a permanent magnet configured to rotate in response to an externally applied non-invasive magnetic field, the permanent magnet operatively coupled to a screw whereby rotation in one direction increases the width between the first and second portions.

In another embodiment, a method of adjusting the spinal canal includes forming first and second bores into a vertebral body, making pedicle cuts to separate a portion of the vertebral body from the pedicles, and securing first and second distraction devices within the first and second bores. The method further includes applying a non-invasive magnetic field to the first and second distraction devices to expand the spinal canal.

In another embodiment, a system for adjusting the spinal canal includes a drilling tool for drilling first and second bores into a vertebral body, a cutting tool for making first and second pedicle cuts to separate a portion of the vertebral body from associated pedicles, and first and second distraction devices configured for placement with the first and second bores. The system further includes an external adjustment device configured to apply a non-invasive magnetic field to the first and second distraction devices, whereby the non-invasive magnetic field distracts both the first and second distraction devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates one embodiment of a pedicle screw system for fusion.

FIG. 1B illustrates a sectional view of a pedicle screw of the pedicle screw system of FIG. 1A.

FIG. 2A illustrates another embodiment of a pedicle screw system for fusion applications.

FIG. 2B illustrates a sectional view of the pedicle screw system of FIG. 2A.

FIG. 3 illustrates another embodiment of a dynamic rod embodiment.

FIG. 4A illustrates a screw.

FIG. 4B illustrates an interbody device according to another embodiment.

FIG. 5 illustrates an artificial disc embodiment.

FIG. 6 illustrates one embodiment of a distraction devices used for vertebral body height adjustment.

FIG. 7 illustrates a top view of one embodiment of a distraction devices used for vertebral body width adjustment.

FIG. 8 illustrates a side view of the embodiment of FIG. 7.

FIG. 9 illustrates an embodiment of a system that includes multiple distraction devices for the selective and incremental expansion of the spinal column.

FIG. 10 illustrates an embodiment of one type of distraction device.

FIG. 11 illustrates an embodiment of another type of distraction device.

FIG. 12 illustrates an embodiment of another type of distraction device. Two of these devices are illustrated in the system of FIG. 9.

FIG. 13 illustrates a perspective view of an external adjustment device.

FIG. 14 illustrates an exploded view of the magnetic handpiece of the external adjustment device of FIG. 13.

FIG. 15 illustrates a first orientation of two magnets of the external adjustment device in relation to an implanted magnet.

FIG. 16 illustrates a second orientation of the two magnets of the external adjustment device in relation to the implanted magnet.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1A illustrates a side view of a pedicle screw-based system 2 for the stabilization of the spine during fusion. The device includes a first pedicle screw 10 disposed in a first vertebral body 11, a second pedicle screw 12 disposed in a second vertebral body 13, and a rod 14 located between the first pedicle screw 10 and the second pedicle screw 12. The rod 14 is fixedly secured at one end to the first pedicle screw 10. The opposing end of the rod 14 is selectively coupled/de-coupled to the second pedicle screw 12 using a magnetic actuator 16, seen in more detail in FIG. 1B. The second pedicle screw 12 includes a screw body 15 having a shank 17 and a spherical head 18. Spherical head 18 has a contact surface 19 which serves as a point of contact when second pedicle screw 12 is coupled to rod 14. As seen in FIG. 1B, the system 2 includes a housing 21 having an end or lip 23 for engaging with the spherical head 18 of the screw body 15 and maintaining the screw body 15 in a particular orientation in relation to the housing 21 when the second pedicle screw 12 is coupled to rod 14. The system 2 includes a magnetic element 28 having a radially-poled magnet 27 bonded within the magnetic element 28. One end of the magnetic element 28 has a coupler 31 which fits into a cavity 29 of a bushing 25. The bushing 25 has a saddle-shaped surface 46 that is shaped to engage with a side surface of the rod 14. The magnetic element 28 can rotate freely with respect to the bushing 25, but coupler 31 transfers axial movement of magnetic element 28 to axial movement of bushing 25 when the coupler 31 makes contact with the bushing 25 inside cavity 29. The magnetic element 28 includes male threads 33 that engage with corresponding female threads 35 located within an inner surface of the housing 21. As seen in FIG. 1B, the magnetic actuator actuates in a direction that is generally perpendicular to the axis of the rod 14. In this manner, the rod 14 is pinched between the bushing 25 and the head 18 of the pedicle screw 12.

The magnetic actuator 16 can be selectively mechanically engaged or disengaged to the second pedicle screw 12 using an externally applied moving magnetic field. For example, one or more rotating or cycling magnets disposed outside the body can be used to selectively engage or disengage the rod 14 to the second pedicle screw 12 by pinching the rod 14 between the bushing 25 and the contact surface 19 of the spherical head 18 of the second pedicle screw 12. The radially-poled magnet 27 may be made from a rare earth magnet, for example Neodymium-Iron-Boron. Because the radially-poled magnet 27 and thus magnetic element 28 are non-invasively rotated by the moving magnetic field, bushing 25 is moved axially to frictionally grip the rod 14 between the contact surface 19 of the spherical head 18 and the bushing 25. A cap 37 having female threads 41 is screwed over male threads 43 of the housing 21 to protect the inner contents. As seen in FIG. 1B, an O-ring seal 39 seals the cap 37 to housing 21. For example, after a fusion procedure has been performed to fuse vertebral bodies 11, 13 together, the subject undergoes radiographic imaging. At this point, the second pedicle screw 12 is engaged with the rod 14. Once evidence of anterior fusion is seen, an external magnetic field is applied (e.g., rotating magnetic field) to disengage or decouple the second pedicle screw 12 from the rod 14. The pedicle screws 10, 12 are no longer providing support and allow posterior movement. This will prevent stress shielding and reduce stresses on adjacent levels. Stress shielding refers to the reduction in bone density (osteopenia) as a result of removal of normal stress from the bone by an implant (for instance, the femoral component of a hip prosthesis). This is because by Wolff's law, bone in a healthy person or animal will remodel in response to the loads it is placed under. Therefore, if the loading on a bone decreases, the bone will become less dense and weaker because there is no stimulus for continued remodeling that is required to maintain bone mass.

This technology could be utilized to “decouple” the rod/screw interface to minimize or eliminate the stress shielding post fusion. This decoupling could provide the same benefit as surgical removal but without the need for a reoperation to remove the hardware post fusion. The stress shielding of the fused level may also contribute to adjacent level disease. If the screws/rods were decoupled there is the possibility that the fused level would induce less stress on the adjacent level and minimize adjacent level disease. Once disengaged, an external magnetic field may be applied again to once again engage the second pedicle screw 12 to the rod 14, locking in a new configuration with a lower stress.

Alternatively, the device may be implanted into two vertebral bodies 10, 12 that have not been fused. This embodiment provides support and possible height restoration while the injured and/or diseased spinal segment heals. As healing occurs, the same or similar device can be used to introduce motion back to the spinal segment in the manner of an internal brace. If pain recurs, the surgeon can re-tighten pedicle screws to support the spine again. Initial implantation of the pedicle screws/rods can be set either rigid or flexible. The flexibility is adjusted post-operatively either increased or decreased based on the patient healing and pain levels.

FIGS. 2A and 2B illustrate another system 20 to control the loading of an interbody fusion to better promote fusion. Traditional pedicle screws may offload discs substantially. There is a general consensus in the medical community that fusion requires some degree of compression to fully form. The system 20 described herein includes two pedicle screws 22, 24 that are connected together via an adjustable rod 26. The adjustable rod 26 is able to shorten (direction of facing arrows A) to apply a compressive load to the vertebral bodies to aid in fusion. The adjustable rod 26 may also be lengthened to reduce this compressive load. The system 20 may be adjusted repeatedly to apply multiple applications of a compressive load to the vertebral bodies if needed. For this system 20, interbody and pedicle screw fixation are conducted as normal however, the two pedicle screws 22, 24 are interconnected to one another via the adjustable rod 26. The adjustable rod 26 includes an outer housing 55 that is secured to the pedicle screw 22 and includes a threaded shaft 53 that is fixedly secured to one end thereof and extends inwardly within the outer housing 55. The adjustable rod 26 further includes a hollow magnetic assembly 69 that is disposed within the outer housing 55 and includes a hollow magnetic element 45 disposed therein, the hollow magnetic assembly 69 having an internal threaded surface 51 engaged with external threads 73 of the threaded shaft 53, the magnetic assembly 69 being coupled to the other of the first pedicle screw and the second pedicle screw

The hollow magnetic element 45 is preferably a radially-poled hollow magnet and effectuates rotation of the hollow magnetic assembly 69 that, for example, rotates in response to an externally applied moving magnetic field. The hollow magnetic assembly 69 may be formed by the hollow magnetic element 45 contained on or within a rotatable cylinder 47. The rotatable cylinder 47 has a hollow cavity 49 into or on which is bonded a nut 71 that contains the threaded surface 51. The nut includes internal threads 51 that engage with a correspondingly threaded shaft 53 which is fixedly attached to outer housing 55, for example, at weld joint 57. The outer diameter of the rotatable cylinder 47 may include an optional o-ring 59, which seals to the inner diameter of outer housing 55. The rotatable cylinder 47 is longitudinally locked to the inner shaft 61 via a rotational coupling or swivel 63. A first pedicle screw 22 is attached to the outer housing 55 and a second pedicle screw 24 is attached to the inner shaft 61 during surgery. The inner shaft 61 is telescopically adjustable within the outer housing 55. The rotation of the radially-poled hollow magnetic element 45 contained in or on the rotatable cylinder 47 of the adjustable rod 26 is then translated into axial shortening or lengthening of the adjustable rod 26. A thrust bearing 65 is held between inner shaft 61 and rotatable cylinder 47, and supports the axial load if the adjustable rod 26 is adjusted in compression (applying distraction between vertebral bodies). An externally applied magnetic field may be applied using an external adjustment device of the type described herein.

Once implanted in the subject, if radiographic evidence of non-fusion or pseudo-fusion exists then the surgeon can adjust the pressure on the fusion site by shortening the adjustable rod 26 and thereby moving the pedicle screws 22, 24 closer to one another to apply a compressive force between the vertebral bodies. The amount of shortening of the adjustable rod 26 will vary the degree of compression applied to the vertebral bodies. An alternative manner of assessing the degree of fusion is by supplying a strain gauge or other force measurement sensor on the adjustable rod, and non-invasively assessing the level of this force over time.

FIG. 3 illustrates another embodiment of a system 30 that includes two pedicle screws 32, 34 and a flexible body or spacer 36 that separates the two pedicle screws 32, 34. The flexible spacer 36 has at one end a magnetic element 38 that interfaces with a cord or rod 40 that extends within the flexible spacer 36. Movement of the magnetic element 38 (e.g., rotation) in response to an applied external magnetic field sets the tensions of the cord or rod 40 and pedicle screws 32, 34. Thus, the tension of the cord or rod 40 as well as the flexible spacer 36 can be controlled in a non-invasive manner. The tension on the cord or rod 40 may be adjusted by the externally applied magnetic field, in order to limit or delimit the amount of motion.

FIG. 4B illustrates another embodiment of a system 50 that includes an adjustable screw 52 with threads on opposing ends much in the manner of a Herbert screw (FIG. 4A). The pitch of each threaded end is different from each other. In this embodiment, as seen in FIG. 4B, a single adjustable screw 52 includes a moveable segment or portion 54 that moves axially relative to a second segment or portion 56. An internal magnet 58 disposed in the adjustable screw 52 rotates in response to an applied external magnetic field thereby causing axial movement of the moveable segment 54 relative to the other portion 56. For example, the adjustable screw 52 can increase in length (arrow B), thereby creating distraction between vertebral bodies. The degree of distraction (or compression) can be altered as needed. This system 50 may be used in conjunction with fusion applications where adjustment is needed to apply compression or other forces to the fused vertebra. This is also useful in two level procedures to adjust one or both levels as this is very difficult to control using current devices and methods.

FIG. 5 illustrates another embodiment of an artificial disc 60 that is adjustable in two directions. A significant effort has gone on into the development of artificial discs. A key design feature of almost all artificial discs is to mimic the natural motion of the spine. A critical feature of artificial discs is the center of rotation (COR) and where it is located. While much work has gone into precisely calculating the COR of implants, in practice, trying to place the artificial disc and lining up the COR is nearly impossible. Quite often the surgeon has missed placement either lateral/medial and/or anterior/posterior. This misplacement is very difficult or impossible to correct.

There is a need post-implantation of an artificial disc to adjust the COR. FIG. 5 illustrates one such artificial disc 60 that includes an x-y adjustment feature built therein. The adjustment feature includes two orthogonal adjustment members 62, 64 that are able to move the body of the artificial disc 60 in the x and y directions. The adjustment members may lengthen or shorten based on a rotational magnet 66 contained in each adjustment member. Application of an external magnetic field is able to adjust each adjustment member. Preferably, each adjustment member can be independently adjusted by a single external adjustment device.

Ideally, the adjustment would be done with the aid of a fluoroscope. The medial to lateral positioning is relatively straight forward and can be done while the patient is in a standing position. For the A/P positioning, the patient could go through flexion and extension motion and the surgeon can monitor the movement of the vertebra relative to the disc and adjust accordingly. This would ensure ideal alignment of the COR of the implant.

FIG. 6 illustrates a distraction device 302 configured for distraction between a first vertebral body 400 and a second vertebral body 402. Intervertebral disks can degenerate, bulge, herniate or thin, and cause accompanying back pain. In this embodiment, the distraction device 302 is inserted between adjacent vertebral bodies 400, 402 and using an external adjustment device (described below) is used to adjust the height of the distraction device 302 to the desired level. This distraction device 302 can distract the vertebral body (e.g., vertebral body 400) to the correct height. Subsidence is a common problem resulting in the loss of disc height over time. After implantation, the distraction device 302 can be adjusted post-operatively using an external adjustment device to restore disc height. The adjustments may be performed intermittently or periodically as required. The adjustments are preferably made after implantation but prior to complete fusion of the affected vertebral bodies.

The distraction device 302 contains a first portion 307 and a second portion 309 and an internal, permanent magnet 304 that can be rotated in response to an applied external magnetic field via an external adjustment device 180 as seen in FIGS. 13 and 14. Internal magnet 304 is coupled to lead screw 306 so that rotation motion changes the displacement between lead screw 306 and the female thread 308 inside the first portion 307 of the distraction device 302 (although the configuration could be reversed). Rotation of the lead screw 306 in one direction causes the first portion 307 and the second portion 309 to separate from one another, thereby increasing the height between the same and the attached vertebral bodies 400, 402. Rotation of the lead screw 306 in the opposite direction causes the first portion 307 and second portion 309 to move closer together, thereby decreasing the height between the same and the attached vertebral bodies 400, 402.

FIGS. 7 and 8 illustrate another embodiment a distraction device 310. This embodiment of the distraction device 310 is used for width adjustment. A wider interbody device provides better clinical results by providing additional stability and minimizing subsidence issues. In this embodiment, the distraction device 310 has a fixed height but can be distracted using an external adjustment device 180 like that seen in FIGS. 13 and 14 to provide a variable width. The distraction device 310 of FIGS. 7 and 8 is oriented between a first vertebral body 400 and a second vertebral body 402, as best seen in FIG. 8, and is generally perpendicular with the orientation of the device 302 of FIG. 6. Distraction of the device 310 will expand the width between the vertebral bodies 400, 102. Like the prior embodiment, there is a first portion 311 and a second portion 313 and an internal, permanent magnet 312 that can be rotated in response to an applied external magnetic field via an external adjustment device 180. The internal magnet 312 is coupled to a lead screw 314 so that rotational motion changes displacement between lead screw 314 and a female thread 316 located inside the first portion 311 of the distraction device 310. The distraction device 310 has a fixed height which provides for a small interbody implant to be inserted. However, the adjustability of the width of the distraction device 310 and the vertebral bodies 400, 402 containing the same provides for increased stability. Also illustrated are pedicles 336, 338 and the spinal canal 410. The distraction device 310 generally distracts in a direction that is substantially perpendicular to the longitudinal axis of the spinal canal 410.

FIG. 9 illustrates another embodiment of a system 330 that includes multiple distraction devices 332 for the selective and incremental expansion of the spinal canal 410. In this embodiment, two distraction devices 332 are located within respective bores 334 formed in each pedicle 336, 338 of a single vertebral body 400. The bores 334 may be formed using conventional drilling tools and techniques. After the bores 334 have been formed, circumferential pedicle cuts 340 are made in each pedicle 336, 338 (i.e., osteotomy). The circumferential pedicle cuts 340 are made by a rotating cutting tool such as a burr (not shown) that is placed within each bore 334. The circumferential pedicle cuts 340, once made, completely separate a portion of the vertebral body 400 from the respective pedicles 336, 338. The two distraction devices 332 are secured within the respective bores 334. The distraction devices 332 may be secured using an adhesive, cement, threads that engage bone tissue or fasteners (e.g., screws or the like).

Utilizing the Ilizarov technique of bone lengthening, only a small gap in each pedicle 336, 338 is left after installation of the distraction devices 332. As the cut pedicles 336, 338 begin to grow back together, each distraction device 332 is expanded incrementally at a rate of approximately one (1) millimeter per day. Each incremental expansion of the distraction devices 332 progressively opens up the spinal canal 410. This is accomplished using the external adjustment device 180 described herein. The adjustments are performed while the subject is awake to provide feedback regarding symptom relief. For example, after adjustment the subject may move his or her spine through one or more motions to determine the degree to which expansion of the spinal canal 410 has reduced discomfort or pain. Additional adjustments of the distraction devices 332 may be made daily or periodically until the spinal canal 410 has been opened up enough to provide the subject with the desired amount of pain or discomfort relief. As part of the periodic adjustment, the subject may go through one or more range of motions to give direct feedback on pain and discomfort levels. Once the desired endpoint has been reached, additional adjustments can be stopped at which point the cut pedicles 336, 338 will undergo a period of consolidation and fully form into a solid bone mass. FIG. 9, illustrates distraction devices 332 of the type illustrated in FIG. 12 secured within bores 34 although other distraction devices 332 may be used in connection with the procedure.

FIG. 10 illustrates one embodiment of a distraction device 332 that includes a moveable segment or portion 342 that moves axially relative to a second segment or portion 344. An axially-poled internal magnet 346 disposed in the distraction device 332 rotates in response to an applied external magnetic field thereby causing axial movement of the moveable segment 342 relative to the other portion 344. The moveable segment 342 contains threads 343 on a portion thereof that interface with corresponding threads 345 disposed on the second portion 344. Rotation of the moveable segment 42 relative to the second portion 44 results in axial displacement of the distraction device 332. For example, the distraction device 332 can increase in length (arrow B), thereby creating a distraction force. The degree of distraction (or compression) can be altered as needed. Threads 348, 350 are located at the respective ends of the moveable segment 342 and the second portion 344 which can be used to engage bone tissue.

FIG. 11 illustrates another embodiment of a distraction device 332. The distraction device 332 includes first and second portions 352, 354 that include respective recesses 356, 358 that contain a rotatable, axially-poled permanent magnet 360. The permanent magnet 360 is coupled to or may include a threaded portion 362 that engages with corresponding threads 364 in one of the first and second portions 352, 354. Rotation of the rotatable permanent magnet 360 extends the first and second portions 352, 354 away from one another, thereby increasing the distraction force. As seen in FIG. 11, the ends of the first and second portions 352, 354 may include threads 366, 368 which can be used to engage bone tissue within each bore 334.

FIG. 12 illustrates another embodiment of a distraction device 332. The distraction device 332 includes first and second portions 370, 372 each having respective threads 374, 376 at an end thereof for mounting the distraction device 332 with the each bore 334 as described above. The first and second portions 370, 372 include respective recesses 378, 380 that contain a rotatable permanent magnet 382. The permanent magnet 382 is coupled to or may include two threaded portions 384, 386 that engage with corresponding threads 388, 390 in the first and second portions 370, 372. In the embodiment of FIG. 12, the distraction device 332 includes one or more guides 394 that extend between the first and second portions 370, 372. The guides 394 prevent relative rotation between the first and second portions 370, 372 yet still permit elongation of the distraction device 332. For example, a plurality of guides 394 could be located circumferentially about the first and second portions 370, 372 to prevent relative rotation.

FIG. 13 illustrates an external adjustment device 180 which is used to non-invasively adjust the devices and systems described herein. The external adjustment device 180 includes a magnetic handpiece 178, a control box 176 and a power supply 174. The control box 176 includes a control panel 182 having one or more controls (buttons, switches or tactile, motion, audio or light sensors) and a display 184. The display 184 may be visual, auditory, tactile, the like or some combination of the aforementioned features. The external adjustment device 180 may contain software which allows programming by the physician.

FIG. 14 shows the detail of the magnetic handpiece 178 of the external adjustment device 180. As seen in FIG. 14, there are two (2) magnets 186 that have a cylindrical shape. The magnets 186 are made from rare earth magnets. The magnets 186 are bonded or otherwise secured within magnetic cups 187. The magnetic cups 187 include a shaft 198 which is attached to a first magnet gear 212 and a second magnet gear 214, respectively. The orientation of the poles of each the two magnets 186 are maintained in relation to each other by means of the gearing system (by use of center gear 210, which meshes with both first magnet gear 212 and second magnet gear 214).

The components of the magnetic handpiece 178 are held together between a magnet plate 190 and a front plate 192. Most of the components are protected by a cover 216. The magnets 186 rotate within a static magnet cover 188, so that the magnetic handpiece 178 may be rested directly on the patient, while not imparting any motion to the external surfaces of the patient. Prior to distracting the intramedullary lengthening device 110, the operator places the magnetic handpiece 178 over the patient near the location of the cylindrical magnet 134. A magnet standoff 194 that is interposed between the two magnets 186 contains a viewing window 196, to aid in the placement. For instance, a mark made on the patient's skin at the appropriate location with an indelible marker may be viewed through the viewing window 196. To perform a distraction, the operator holds the magnetic handpiece 178 by its handles 200 and depresses a distract switch 228, causing motor 202 to drive in a first direction. The motor 202 has a gear box 206 which causes the rotational speed of an output gear 204 to be different from the rotational speed of the motor 202 (for example, a slower speed). The output gear 204 then turns a reduction gear 208 which meshes with center gear 210, causing it to turn at a different rotational speed than the reduction gear 208. The center gear 210 meshes with both the first magnet gear 212 and the second magnet gear 214 turning them at a rate which is identical to each other. Depending on the portion of the body where the magnets 186 of the external adjustment device 180 are located, it is desired that this rate be controlled, to minimize the resulting induced current density imparted by magnet 186 and cylindrical magnet 134 though the tissues and fluids of the body. For example a magnet rotational speed of 60 RPM or less is contemplated although other speeds may be used such as 35 RPM or less. At any time, the distraction may be lessened by depressing the retract switch 230. For example, if the patient feels significant pain, or numbness in the area holding the device.

FIGS. 15 and 16 illustrate the progression of the magnets 186 (individually numbered) 1134 and 1136) and the implanted magnet 1064 that is located within the distraction device during use. Implanted magnet 1064 is shown for illustration purposes. Implanted magnet 1064 is one possible embodiment of the magnetic element described herein. FIGS. 15 and 16 illustrate the external adjustment device 180 being disposed against the external surface of the patient's skin 1180 adjacent the spine. In the non-invasive adjustment procedure depicted, the patient 100 lies in a prone position, and the external adjustment device 180 is placed upon the patient's back. However, the adjustment is conceived possible with the patient in supine, standing or positions. The external adjustment device 180 is placed against the skin 1180 in this manner to remotely rotate the implanted magnet 1064. As explained herein, rotation of the implanted magnet 1064 is translated into linear motion to controllably adjust the distraction device.

As seen in FIGS. 15 and 16, the external adjustment device 180 may be pressed down on the patient's skin 1180 with some degree of force such that skin 1180 and other tissue such as the underlying layer of fat 1182 are pressed or forced into the recess 1174 of the external adjustment device 180. FIGS. 15 and 16 show the magnetic orientation of the implanted magnet 1064 as it rotates in response to rotation of the permanent magnets 1134, 1136 of the external adjustment device 180.

With reference to FIG. 15, the implanted magnet 1064 is shown being oriented with respect to the two permanent magnets 1134, 1136 via an angle θ. This angle θ may depend on a number of factors including, for instance, the separation distance between the two permanent magnets 1134, 1136, the location or depth of where the implanted magnet 1064 is located, the degree of force at which the external adjustment device 180 is pushed against the patient's skin. Generally in applications including some obese patients, the angle θ should be at or around 90° to achieve maximum drivability (e.g., torque).

FIG. 15 illustrates the initial position of the two permanent magnets 1134, 1136 and the implanted magnet 1064. This represents the initial or starting location (e.g., 0° position as indicated). Of course, it should be understood that, during actual use, the particular orientation of the two permanent magnets 1134, 1136 and the implanted magnet 1064 will vary and not likely will have the starting orientation as illustrated in FIG. 15. In the starting location illustrated in FIG. 15, the two permanent magnets 1134, 1136 are oriented with their poles in an N-S/S-N arrangement. The implanted magnet 1064 is, however, oriented generally perpendicular to the poles of the two permanent magnets 1134, 1136.

FIG. 16 illustrates the orientation of the two permanent magnets 1134, 1136 and the implanted magnet 1064 after the two permanent magnets 1134, 1136 have rotated through 90°. The two permanent magnets 1134, 1136 rotate in the direction of arrow A (e.g., clockwise) while the implanted magnet 1064 rotates in the opposite direction (e.g., counter clockwise) represented by arrow B. It should be understood that the two permanent magnets 1134, 1136 may rotate in the counter clockwise direction while the implanted magnet 1064 may rotate in the clockwise direction.

During operation of the external adjustment device 180, the permanent magnets 1134, 1136 may be driven to rotate the implanted magnet 1064 through one or more full rotations in either direction to increase or decrease distraction of the device as needed. Of course, the permanent magnets 1134, 1136 may be driven to rotate the implanted magnet 1064 through a partial rotation as well (e.g., ¼, ⅛, 1/16, etc.). The use of two magnets 1134, 1136 is preferred over a single external magnet because the implanted magnet 1064 may not be oriented perfectly at the start of rotation, so one external magnet 1134, 1136 may not be able to deliver its maximum torque, which depends on the orientation of the internal driven magnet 1064 to some degree. However, when two (2) external magnets (1134, 1136) are used, one of the two 1134 or 1136 will have an orientation relative to the internal driven magnet 1064 that is better or more optimal than the other. In addition, the torques imparted by each external magnet 1134, 1136 are additive.

While embodiments of the present invention have been shown and described, various modifications may be made without departing from the scope of the present invention. As one example, the devices described herein may be used to lengthen or reform a number of other bones such as the mandible or the cranium. The invention, therefore, should not be limited, except to the following claims, and their equivalents. 

What is claimed is:
 1. A method for adjusting the amount of compression between two vertebral bodies, the method comprising: securing a first pedicle screw to a first vertebra; securing a second pedicle screw to a second vertebra; securing an adjustable rod to the first pedicle screw and the second pedicle screw, the adjustable rod comprising: an outer housing, wherein the outer housing includes a threaded shaft secured to one end thereof and extending along an interior portion thereof; an inner shaft, wherein at least a portion of the inner shaft is telescopically adjustable within the outer housing; a hollow magnetic assembly disposed within the inner shaft and comprising a hollow magnetic element, the hollow magnetic element disposed around at least a portion of the threaded shaft, the hollow magnetic assembly having an internal threaded surface engaged with the threaded shaft, the hollow magnetic assembly rotatably coupled to the second pedicle screw by a rotational coupling; and a thrust bearing disposed between the magnetic assembly and the second pedicle screw; and applying an external magnetic field to the adjustable rod to rotate the magnetic element.
 2. The method of claim 1, further comprising: decreasing an amount of compression between the two vertebral bodies.
 3. The method of claim 1, further comprising: increasing an amount of compression between the two vertebral bodies.
 4. The method of claim 1, further comprising: assessing a degree of fusion between the two vertebral bodies.
 5. The method of claim 4, wherein the degree of fusion is assessed radiographically.
 6. The method of claim 4, wherein the degree of fusion is assessed by measurement of a force by the adjustable rod.
 7. The method of claim 4, wherein the hollow magnetic assembly comprises a hollow cylindrical radially-poled magnet.
 8. The method of claim 7, wherein the hollow cylindrical radially-poled magnet comprises a rare earth magnet.
 9. The method of claim 4, wherein the internal threaded surface of the hollow magnetic assembly comprises a nut coupled to an internal surface of the hollow magnetic assembly.
 10. The method of claim 4, further comprising an external adjustment device configured to apply the external magnetic field.
 11. The method of claim 4, wherein the external magnetic field comprises a rotating magnetic field. 